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Writing Limits

  1. Oct 8, 2013 #1
    so solving lim's can be tedious not because they are hard but because you have to continously keep writing lim x->a while solving the equation is there a mathematical shortcut to writing limits without keep writing lim x->a all the time after each development???

    thanks.
     
  2. jcsd
  3. Oct 8, 2013 #2

    UltrafastPED

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    You can develop your own private notation for your private notes ... for example just draw an underline, and make a note as to what it means.
     
  4. Oct 8, 2013 #3
    i know, but i meant for the exam will => do the trick?
     
  5. Oct 8, 2013 #4

    Office_Shredder

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    On an exam you are likely to be expected to write [itex]\displaystyle \lim_{x\to a} [/itex] on every single line, unless you are actually writing something down which is not a limit. Your instructor's opinion may vary (you should ask them if you feel it's really important), but I find it unlikely. There are two reasons for this

    1.) Writing six characters four or five times doesn't take that much time.
    2.) A LOT of students don't understand what limit notation actually means, so instructors absolutely need to grade on correctness here.
    3.) You should never write down things which are not mathematically true on an exam, and this is no exception.
     
    Last edited: Oct 8, 2013
  6. Oct 8, 2013 #5

    Mark44

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    A significant amount of the work in evaluating a limit is manipulating the expression so that you can actually take the limit. For these preliminary steps, since you haven't taken the limit yet, it's important that you include the "lim x -> a" part.
     
  7. Oct 9, 2013 #6

    HallsofIvy

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    Quite frankly, if the hard part is writing the "[itex]\lim_{x\to a}[/itex]" you must be brilliant- and painfully lazy!
     
  8. Oct 9, 2013 #7
    If your algebra goes [itex]\lim_{x\to a}f(x)=\lim_{x\to a}g(x)=\lim_{x\to a}h(x)=\lim_{x\to a}k(x)=L[/itex], and if the above equality holds because [itex]f=g=h=k[/itex] everywhere, then you could do your algebra in two steps:
    - [itex]\forall x, \enspace f(x)=g(x)=h(x)=k(x)[/itex].
    - Therefore [itex]\lim_{x\to a}f(x)=\lim_{x\to a}k(x)=M[/itex].
     
  9. Oct 11, 2013 #8
    some of the lims get a bit complicated and keep writing lim x->a all the time like 10 times is a pain in the butt.
     
  10. Oct 14, 2013 #9

    Mark44

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    Then you can do it like economicsnerd suggests below.

     
  11. Oct 14, 2013 #10

    HallsofIvy

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    Yep, that's "painfully lazy"!

    I, on the other hand, am painfully lazy but NOT brilliant.
     
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